Monday, August 26, 2013

Is Acute Back Pain Predictive of Chronic Pain?

Back PainMost persons will experience lower-back pain in their lifetimes and some will progress to a long-term, chronic back pain condition. New research suggests that high pain intensity at onset and a pessimistic outlook are predictive of future pain and disability, even after 5 years; however, the statistical and clinical significance of this study’s findings need careful consideration.

Researchers at Keel University, Staffordshire, England, evaluated 488 primary care practice patients who sought treatment for lower-back pain [Campbell et al. 2013]. The intent of the study was to determine what prognostic factors best predict poor pain and disability outcomes 5 years later, and to compare these factors with short-term outcomes at a 6-month follow-up.

Study subjects were mailed questionnaires soon after their physician visits and were surveyed again after 6 months and at 5 years. Pain and disability were measured using the Chronic Pain Grade, a seven-item chronic pain assessment tool. An array of 32 potentially predictive factors for consideration were organized in 4 categories: demographic, physical, psychological, and occupational.

Writing in the Journal of Pain the researchers report that, after controlling for the many predictive variables, baseline pain intensity conferred a 12% increase in risk (Relative Risk = 1.12, 95% Confidence Interval = 1.03–1.20), and patients' beliefs that their low-back pain would persist conferred a 4% increased risk (RR = 1.04, 95% CI = 1.01–1.07) for poor outcome at 6 months. A poor outcome at 5 years was best predicted by a model with the same factors as at 6 months: pain intensity increased risk by 9% (RR = 1.09, 95% CI = .997–1.20), and a belief that low-back pain would persist increased risk by 6% (RR = 1.06, 95% CI = 1.03–1.09).

The researchers concluded that both predictors — initial pain intensity and belief in pain persistence — have the potential to be targets for clinical interventions to avert chronic pain development. They further noted that this research confirms previous studies asserting that baseline pain intensity is a key predictor of future pain and disability; however, this was the first investigation to demonstrate this association over such a long period of time.

This study suggests that aggressive and effective pain relief during the early management of low-back pain has major implications for long-term outcomes. Also, patient beliefs that pain will persist a long time can affect progression to chronic and disabling low-back pain, independent of a wide range of other prognostic factors. Clinically, this seems reasonable, as patients with lower expectations of recovery may be less adherent to advice and treatments for their back pain.

Statistically, however, the key findings of this study (noted above) are rather weak, as indicated by 95% Confidence Intervals that border on 1.0 at the low ends, and the RRs represent small effect sizes overall. In fact, the increased Relative Risk of 9% poorer outcome at 5 years influenced by initial pain intensity was not actually significant (95% CI = .997–1.20). So the results of this study should be considered with some caution and need verification in other research.

Technical note: What might the study results mean clinically?

In proposing the clinical impact of their findings, Campbell and colleagues write that with the per unit change in score for pain intensity of 12% at 6 months and 9% at 5 years, as indicated by the Relative Risks in their study, “a person with a one-third higher score of baseline pain intensity would have a 44% increase in risk of poor outcome at 6 months and a 33% increase in risk at 5 years.”

Furthermore, for the variable measuring how long the person believes his/her back pain will last — ie, increase in risk of 4% at 6 months and 6% at 5 years per unit change on the scale score — the authors state, “a person with a one-third higher score on the timeline scale at baseline would be at an increase of 32% in risk of poor outcome at 6 months and a 48% increase in risk at 5 years.”

These projections by Campbell et al. appear to be clinically important and significant influences on patient outcome; however, the authors do not indicate how those percentage computations were made and, based on the limited information in their report, we cannot reproduce the findings. We encourage any readers who decipher the math behind those clinical-impact percentages to comment on this below.

REFERENCE: Campbell P, Foster NE, Thomas E, DUN KM. Prognostic Indicators of Low Back Pain in Primary Care: Five-Year Prospective Study. J Pain. 2013(Aug);14(8):873-883 [abstract here].

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